Many homes have programmable thermostats that allow a user to enter multiple settings for running the heat, ventilation and air conditioning (HVAC) systems to match the expected occupancy patterns of the residents to save energy. Most homes also have multiple zones with dedicated HVAC units, each having a separate programmable thermostat. It is generally appropriate to heat or cool different zones on different schedules to save energy. In some homes, for example, it may be appropriate to heat and cool the main living zone during waking hours, while the bedroom zone can be heated and cooled during sleeping hours. It may also be advantageous to turn the thermostats well down (i.e., turn the heating temperature setting up and the air conditioning temperature down) whenever the residents are scheduled to be away from home for extended periods, for example during weekday working hours. The thermostats can be programmed to automatically adjust to more comfortable settings when the residents are scheduled to return home. There may also be special events, such as vacations, when the entire family is away from home for extended periods. When the entire family is away from the home, energy can be saved by turning the thermostats well down for the duration of their absence.
In general, more accurate thermostat programming reflecting the actual occupancy of the residents can save energy, but few homeowners remember to adjust the thermostat as frequently as schedules change. And even if a homeowner were to endeavor to set the thermostats daily to reflect the expected occupancy schedules of the residents, the thermostat settings might still turn out to be less then optimal, at least on some occasions, due to unexpected changes in the schedules.